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Variation in Floor Load and Plate load in staad pro

 
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Moazzam
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PostPosted: Thu Mar 10, 2011 8:15 am    Post subject: Variation in Floor Load and Plate load in staad pro Reply with quote

Dear sifians,

I have analyzed  one of the block of the rcc structure in staad pro using two different methods in Load generation. One is with floor load generation and the other is with plate load generation with the same loads, I observed that the results are different in both cases.
Usually I used Floor Load generation for conventional beam and solid slabs, I thought of checking the results using plate load generation instead of floor load. Can any one please suggest me which one to be fallowed, For more details I am enclosing the staad files.

More ever if you observed the results of one of the column( Beam no.48 as per staad pro) in first method max moment is 1803kN-m and in the second method it is1505KN-m. Since the moment is too high, can i release the moment from secondary beams, Can I design the beams without releasing the moments and columns after releasing the moments. Please suggest.
Or if I am wrong please suggest me the procedure.
I will be thankful to All.



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PREETI_SARKAR
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PostPosted: Fri Mar 11, 2011 9:45 am    Post subject: Reply with quote

I haven't had a chance to look at your models . What program should I use to open a RAR file? It is like a ZIP file I assume.

I assume that the FLOOR LOAD model has only beams and no plates, while the plate load model has beams and plates.

In my opinion, you are getting different results because the plate model includes the stiffness of the plates, while the floor load model has the stiffness of the beams and columns only. So, the plates will also carry some of the load. The total moment will be divided between the beams and the plates in the plate load model, where as, it will be carried entirely by the beams in the floor load model. That is what the moment in the beams is smaller in the plate model. The rest of the moment is taken by plates.

Hope I am right.
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Moazzam
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PostPosted: Fri Mar 11, 2011 12:44 pm    Post subject: Reply with quote

First, I would like to thanks you for giving a reply,

I have compressed the files using winrar which is same as winzip.

Please refer the staad model and suggest me which method to be fallowed,

thanks once again
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Arvind Kumar Jaiswal
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PostPosted: Fri Mar 11, 2011 3:06 pm    Post subject: Reply with quote

Dear friend,

The floor load is the model which does not take in to account the stiffness of floor, so the deformations you get will be commensurate to the model you choose.

Conside the roof plan to aspect ratio less than 3, then you will get may be somewhat near results may be acceptable for small structure, but when the aspect ratio (Length divided by breadth) is more than 3 then your results will not be acceptable altogether.

Hence it is better to follow always plate model (or any model which uses the stiffness of slab in its geometry and gives displacements according to the stiffness of slab), which will give you exact behaviour of the structure as you have modelled.

But E-Tabs has some different methodology and incarporated different routine in software.... Could Rajeev from CSI India explain for the benefit of all?
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rukmangad.garud
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PostPosted: Sat Mar 12, 2011 4:47 am    Post subject: Variation in Floor Load and Plate load in staad pro Reply with quote

The floor load option can be suitable used in staad to distribute the floor load on beams. the effect of rigid diaphragm action of slab in case of seismic analysis can be effectively incorporated by using master slave specification or providing diagonal beam connection of appropriate stiffness.
Using master slave option is more convenient.
Using the plate to model as a slab in staad will require the plate to be meshed (FEM Analysis) and this creates a larger output file.
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Moazzam
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PostPosted: Sat Mar 12, 2011 6:32 pm    Post subject: Reply with quote

Thanks all for valuable support
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